As described in Patent Documents 1 and 2, nitrogen-containing cyclic compounds, typically piperazine are useful as resin additives (specifically epoxy resin curing agents), paint additives, adhesives and the like. Since piperazine has a secondary amine structure, the use of piperazine as a curing agent for epoxy resins, for example, ensures that piperazine ring is introduced into the epoxy resin via reaction of the secondary amine moiety with an epoxy group, for thereby imparting the stiffness, mechanical strength and transparency (inclusive of the UV region) inherent to the piperazine ring structure to the epoxy resin.
However, a problem arises with the piperazine described in Patent Documents 1 and 2 because it has active hydrogen on the nitrogen atom. On use of piperazine as a curing agent for epoxy resins, if piperazine is previously added to an epoxy resin, viscosity buildup and gelation can occur with the lapse of time. It is not viable with a curable composition of one part type. The composition must be formulated as two part type which requires cumbersome operations like accurate weighing and mixing on use.